The invention relates to an integrated circuit for a keyboard of electronic apparatus, comprising pushbutton keys arranged in n columns and m rows, each pushbutton key having two terminals and, when being actuated, directly connects one column line associated with the respective column, to one row line associated with the respective row, with each column line being temporarily connected to the input of a first column inverter and, across a first resistance element, to a constant potential, with each row line, via the clocked current path of a row transistor, being connected to the zero point of the circuit, with a row inverter being associated therewith. An example of such a circuit is disclosed in the German Offenlegungs/Auslegeschrift DE No. 28 54 934 A1/B2 corresponding to U.S. Pat. No. 4,266,213.
In the conventional arrangement the resistance elements associated with each column line, are connected to the zero point of the circuit, and the first column inverters are connected to the respective column line via electronic switches which are periodically opened and closed by a clock signal, so that they are only temporarily connected to one another while the switches are closed. Moreover, in the conventional arrangement one row inverter each is associated with the individual row lines, which are likewise only temporarily in connection with the row lines, i.e., when the electronic switches which are controlled by a clock signal which is inverse in relation to the aforementioned clock signal, are closed. The conventional arrangement operates statically when at normal, hence when the pushbutton keys are not depressed, and operates dynamically when a pushbutton key is depressed, with the number of employed components being very small. Moreover, with respect to the columns, the conventional arrangement supplies a l-ex-n-coded signal and, with respect to the rows, a l-ex-m-coded signal.